1. Field of the Invention
The invention relates to optical waveguide junctions for use in guided-wave optics and in particular to a multimode channel waveguide that is useful for selective mode excitation, routing, switching, modulation, and wavelength multiplexing/demultiplexing.
2. Description of the Prior Art
The use of optical waveguides for transmitting light along the surface of a substrate is well known in the art and a promising technique for the fabrication of integrated optical circuits. Optical waveguide junctions are important elements for performing splitting and recombining of optical signals in guided-wave devices such as interferometers and branching circuits. In particular, it has been shown that asymmetric waveguide Y junctions can be used to spatially separate the modes in a double-mode waveguide, which makes them useful, e.g., in three-port optical switches. See, for example, "Dielectric Thin-Film Optical Branching Waveguide", H. Yajima, Appl. Phys. Lett., Vol. 22, June 15, 1973, pp. 647-649, and "Optical-Waveguide Hybrid Coupler", M. Izutsu, A. Enokihara, T. Sueta, Optics Letters, Vol. 7, No. 11, November, 1982, pp. 549-551. The Yajima reference describes the fabrication of branching waveguides with only two output channels of different widths, and with the same index of refraction. Although such prior art devices are capable of simple mode filtering applications, the demands of complex integrated optical circuits require a much greater degree of signal processing functions. Prior to the present invention, there has not been a suitable technique for the fabrication of waveguide junctions capable of a variety of optical signal processing functions such as selective mode excitation, routing, switching, modulation, and wavelength multiplexing/demultiplexing of guided waves, as well as for mode control in semiconductor lasers.